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NiCuZn · Black Owl — Engineering calculation sheet

Control valve Cv and Kv.

Estimate the required flow coefficient for a liquid control valve, with a check for choked flow and cavitation risk.

Service
m³/h
–

Liquid density relative to water; 1 for water.

bar
bar(a)
Choked flow check
bar(a)

Water at 20 °C is about 0.023 bar(a).

bar(a)

Water is 220.6 bar(a).

–

Typically about 0.9 for globe valves and lower for ball and butterfly valves; use vendor data.

Results

Required Cv23.12 US
Required Kv20 m³/h
Flow conditionNot choked
Choked pressure drop limit4.032 bar
Pressure drop used for sizing1 bar
Liquid critical pressure ratio FF0.957

Preliminary estimate for early engineering. Check against your design basis, standards and vendor data.

Method

How it is calculated

For incompressible, turbulent, non-choked liquid flow:

Kv = Q √(SG / ΔP)  ·  Cv = 1.156 Kv

with Q in m³/h and ΔP in bar. Flow becomes choked when the pressure drop reaches:

ΔPchoked = FL² (P1 − FF Pv)  ·  FF = 0.96 − 0.28 √(Pv / Pc)

Beyond that point extra pressure drop does not increase flow, and cavitation or flashing is expected; the tool sizes with the choked pressure drop and warns. This follows the basic liquid sizing equations of IEC 60534-2-1 without piping geometry or viscosity corrections.

A valve is usually selected so the required Cv falls well inside its range at normal flow, leaving room for maximum flow and control. Confirm the selection, noise and cavitation with the valve vendor.

All engineering tools →Size equipment from your own balance in Black Owl ↗

Calculated with the free engineering tools at nicuzn.com/tools. Preliminary estimate for early engineering; check against your design basis, applicable standards and vendor data before use.